1. Field of the Invention
This invention relates to a speed control system for small medical motors used for dental handpieces and other medical apparatuses.
2. Prior Art
In these days, medical apparatus driven by micromotors are being made smaller as the performance of micro-motors is being improved. Under this situation, dental handpieces driven by micro-motors instead of conventional electric engines or air turbines have been developed. To drive micro-motors, the dropper method by a power transistor has been frequently used. However, the micro-motors for conventional handpiece apparatuses have great speed fluctuation, and cannot deliver stable rotational speed. To solve this problem, current increase under load is detected, and positive-fed back to the control section, preventing speed reduction and keeping a constant speed. However, this attempt has not yet reached satisfactory results, i.e., motor speed decreases or increases excessively as load increases as shown in FIG. 2.